allyne



J; I T 1' 4' Jam, 2% R, :1 ALLY Zflfififlfi? METHOD OF AND APPARATUS FORCONTROLLING THE TEMPERATURE OF TRAILER CARGO AND THE LIKE Original FiledJan. 18, 1950 3 Sheets-Sheet l INVEN T01 2. m RULUN E ALLY NE ATTORNEYS59% R. F. ALLYNE ,731,807

METHOD OF AND APPARATUS FOR CONTROLLING THE TEMPERATURE OF TRAILER CARGOAND THE LIKE Original Filed Jan 18, 1950 3 Sheets-Sheet 2 2 Fig. 0

IN VEN TOR.

ROLLW E ALLYNE BY XMMM ATTORNEYS 24-, 1956 R. F. ALLYNE {731 897 METHODOF AND APPARATUS FOR CONTROLLING THE TEMPERATURE OF TRAILER CARGO ANDTHE LIKE Original Filed Jan. 18, 1950 5 Sheets$heet 3 J U 3 O a u 1 aHlh. mum H I HIIIIH H HIIIII.

IIII'IIIL INVENTOR.

ROLLIN E ALLYNE BY 9 gw im WW ATTORNEYS United States Patent METHOD OFAND APPARATUS FOR CONTROL- LING THE TEMPERATURE OF TRAILER CARGO AND THELIKE Rollin F. Allyne, Newport News, Va.

Original application January 18, 1950, Serial No. 139,272

now Patent No. 2,589,031, dated March 11, 1952. Divided and thisapplication January 10, 1952, Serial No. 265,763

9 Claims. (Cl. 62--6) This invention relates to a method of andapparatus for controlling the temperature of trailer cargo and the like,and also to a refrigeration unit for truck trailers and the like,particularly adapted to contain a solid deliquescent or sublimatingrefrigerant, such as solid carbon dioxide or Dry Ice. This applicationis a division of my co-pending application Serial No. 139,27), filedJanuary 18, 1950, now U. S. Patent 2,589,031, granted March 11, 1952.

In the transportation of all perishables requiring protection againstheat or cold, particularly in the case of relatively large trailersdrawn by a tractor, the time during which the commodity is in thetrailer during a cross country run may be several days. Many of theseruns are substantially non-stop, and the temperature variations areusually considerable. For instance, in a run between Denver and LosAngeles, the temperature when the trailer is passing over the mountains,both west of Denver and east of Los Angeles, is usually considerablylower than when crossing the arid and/or desert country in between.Furthermore, the difference between the day and night temperatures inarid or desert country is usually large. Thus, during a large portion ofthe run, refrigeration is necessary for the transportation of meats,vegetables and the like. However, since food is normally moved topopulation centers, and non-perishables are normally moved away frompopulation centers, it often happens that refrigeration will benecessary for the cargo carried in one direction, but will beunnecessary for the cargo carried on the reverse trip. Again, duringwinter months the outside temperatures, as over mountain passes, i

may be sutficiently low so that certain perishable items might tend tofreeze and thereby become damaged, so that it is sometimes necessary tosupply heat to the cargo.

Mechanical refrigeration equipment has been developed which may beinstalled in a truck body, trailer or the like, to cool the cargoadequately and maintain the desired temperature. However, the weight ofsuch mechanical equipment is fixed, and oftentimes on a run on which thenature of the cargo is such that refrigeration is unnecessary, suchweight materially reduces the pay load which may be carried by the truckor trailer. Also, the initial and maintenance costs of such equipmentare relatively high, and its use only during a part of the time addsmaterially to the actual cost of maintaining the desired temperature ofthe cargo. Water ice is not a suitable refrigerant for such cargoes,since the melting point of ice is +32 F., and the temperature to whichair may be cooled by passing over such ice is generally limited to above32. Thus, since some of the cargoes carried are frozen and others mustbe maintained at a temperature below +32 F., water ice is anunsatisfactory refrigerant.

Solid carbon dioxide, which deliquesces or sublirnates, i. e. changesfrom the solid to the gaseous state, at about l12 F. at one atmospherepressure, is suitable for cooling air to a temperature below that towhich any perishable or frozen cargo must be cooled or maintained.Thus,,if a supply of solid carbon dioxide sufficient to last PatentedJan. 24, 1956 for a predetermined period, can be loaded in a truck ortrailer at the start of a trip, the weight will decrease during thetrip. Also, the total weight of the refrigeration equipment is much lessthan mechanical refrigeration equipment when cooling is not needed.However, because of its extremely low temperature, previous attempts toutilize solid carbon dioxide as a refrigerant for maintaining a cargocool in a truck body or trailer have not been entirely satisfactory,because of lack of adequate control of the cooling efliect, localizedfreezing of portions of the cargo, and for other reasons. Thus, if anattempt is made to transfer heat directly from the cargo to the solidcarbon dioxide, that portion of the cargo nearest to the cooling unittends to be unduly cooled, which is particularly disadvantageous in thecase of certain perishable vegetables. If one portion of the cargo iscooled considerably more than necessary, the entire operation isineflicient since the maximum temperature of other portions of the cargomust be reduced to a desired point. Furthermore, if a container of solidcarbon dioxide is merely placed in the cargo space, but positioned apartfrom any cargo, air cooled to an extremely low temperature tends to movedownwardly from the cooling unit and settle in the bottom of the cargospace, thereby tending to freeze the lower portion of the cargo andpermit the upper portion to remain at an undesirably high temperature.Previous attempts to provide adequate circulation of the cooling airhave not been entirely satisfactory.

In addition to the long hauls, or cross country runs, there are shorthauls, such as involving delivery trucks and the like, and the problemof adequate cooling, more nearly uniform temperature, and maintenance ofcooling capacity are again of importance. Thus, it is important that allparts of a cargo be maintained sufiiciently cold, and that heat loss dueto the frequent opening and closing of doors be compensated. Inaddition, since the outside temperature is normally higher in theafternoon than the morning, for instance, it is necessary that adequatecooling capacity be present later in the day as well as earlier.

Among the objects of the present invention are to provide a novel methodof controlling the temperature of a trailer cargo or the like; toprovide such a method which is particularly useful in cooling cargo bymeans of a low temperature refrigerant, such as solid carbon dioxide; toprovide such a method by which the cargo is cooled indirectly, as byutilizing air as a heat transfer medium; to provide such a method bywhich undue cooling or freezing of any portion of the cargo iseliminated; to provide such a method by which all portions of the cargomay be maintained at or about the same temperature, within limits of afew degrees; to provide novel apparatus for controlling the temperatureof a trailer cargo or the like, and particularly adapted to carry outthe above method; to provide such apparatus which is particularlyadapted to be installed in a trailer, truck body, or other cargo spaceto provide temperature control during transportation; to provide suchapparatus which may also be utilized in cooling down a cargo which iswarm when loaded; to provide such apparatus by which adequatecirculation of cooled air is obtained; to provide such apparatus whichprevents the freezing or undue cooling of any portion of the cargo; toprovide such apparatus which can also be utilized in conjunction with aheater for heating the cargo; to provide such apparatus which includes anovel cooling or refrigeration unit for a solid refrigerant, such assolid carbon dioxide; to provide such a refrigeration unit particularlyadapted to cool air passed along the exterior thereof; to provide such aunit which may be made readily accessible for loading of solid carbondioxide therein; to provide such a unit, the cooling capacity of whichremains substantially constant, between the time a full grease? chargeof solid carbon dioxide cakes are placed therein and the time at whichthese cakes have almost disappeared; to provide such apparatus which maybe accurately controlled; to provide such apparatus which may beconstructed in more than one form; to provide such apparatus which maybe made comparatively light in weight, so that the pay load of the truckbody or trailer may be a maximum when refrigeration is not required; andto provide such apparatus which will be efiicient in operation andrelatively cheap to construct, install, and maintain.

Additional objects and the novel features of this invention will becomeapparent from the following description, taken in connection with theaccompanying drawings, in which:

Fig. 1 is a perspective view of a trailer provided with cargotemperature control apparatus constructed in accordance with thisinvention, and by which the method of this invention may be carried out;

Fig. 2 is a vertical section taken centrally at the forward end of thetrailer of Fig. 1, also showing in vertical section a solid refrigerantunit constructed in accordance with this invention;

Fig. 3 is a horizontal section taken along line 3-4: of Figure 2;

Fig. 4-is an enlargement of a portion of Fig. 3, showing moreparticularly details of construction of the refrigeration unit, at aforward corner thereof;

Fig. 5 is a fragmentary vertical section illustrating a construction ofa portion of the refrigeration unit, alternative to that shown in Fig.2;

Fig. 6 is a front elevation of a blower unit and a heating unit, whichare installed above the refrigeration unit, and taken generally from theposition of line 6--6 of Fig. 2;

Fig. 7 is an end view of the blower and heating units of Fig. 6, showingalso a portion of the front wall of the trailer;

Fig. 8 is a wiring diagram illustrating a cooling control circuit forthe motor of the blowers of Fig. 6;

Fig. 9 is a wiring diagram illustrating a control circuit for the heaterunit which may be added to or incorporated in the cooling controlcircuit; and v Fig. 10 is a vertical section, similar to Fig. 2,illustrating an embodiment of this invention claimed in saidPatent-2,589,031. I

As illustrated in Fig. 1, the method of this invention may be carriedout by utilization of the apparatus installed in a control space S, atthe forward end of a trailer T which carries a load or cargo C. Thecargo C is illustrated as a solid body of material, shown in dottedoutline in Fig. 1 and in section in Figs. 2, 3 and 10,

it being understood that when the cargo is a number of cartons, forinstance, which may be packed close together, the cargo C may occupy allof the space indicated, but since the cargo often consists of separatepieces of irregular shape, such as hanging meat or the like, there maybe air passages to a greater or less extent between the various parts ofthe cargo. However, a solid cargo, that is, a cargo which is packed sothat there are substantially no air passages between the pieces orparts, is generally the most difficult to maintain cool, or to heat, sothat it will be substantially uniform at all points.

The cargo C is preferably placed in the trailer T to provide a space itabove the cargo, between the cargo and the roof 11 of the trailer T andextending from front to rear, a space 12 between the rear end of thecargo C and the rear doors 13 of the trailer, as well as spaces'betweenthe sides of the cargo and the respective side walls 14- and 15 of thetrailer. In addition, the cargo is preferably placed on racks 16, whichmay consist of diagonally extending panels or plates, preferably spacedapart and mounted on longitudinally extending bars, to provide airpassages between the bottom of the cargo and the floor 17 of thetrailer. The roof 11, rear doors 13, sides 14 and l 15,, floor 17 andthe front wall 18 of the trailer are preferably double walled andinsulated in a conventional manner, as shown.

The temperature control space S may be formed by the partition P, spacedfrom the front wall 18 of the trailer a suflicient distance toaccommodate a refrigerant unit or bunker B, adapted to contain a solidrefrigerant such as Dry Ice, i. e. solid carbon dioxide. Partition P, asin Fig. 2, is preferably provided with insulation 1? up to at least thetop of the bunker B, so as to prevent any cargo on the opposite side ofthe partition P from being unduly cooled. The partition P is preferablysolid and air tight, except that the lower end is preferably spaced fromthe floor 17 of the trailer, to provide a passage 20 for air to be drawnfrom the cargo space, upwardly past the bunker B, such air thereby beingcooled, and then discharged into the space above the cargo by a pair ofblowers 21 driven by a motor 22, mounted above the bunker. As indicatedby the arrows of Fig. 1, the cooled air may be discharged through vents23 in partition P, so as to be propelled rearwardly through space 10along the top of the cargo, some of the air passing downwardly along thesides of the cargo, in the spaces next to the sides 14 and 15 of thetrailer, and the remainder of the air passing over the rear of thecargo, down through the space 12 adjacent rear doors 13. The air thenmoves through the passages beneath the racks E6, to the passage 20between the partition P and the floor 13, for recirculation. Such airflow, of course, may take place only during the cooling periods, i. e.when the temperature of the cargo space reaches the high setting of athermostat, such as including a bulb 24 in the position of Fig. 2, anduntil the low setting is reached. Since adequate contact of the air withthe cargo can be obtained by such circulation, the temperature atthermostat bulb 2.4 will correspond to the temperature of the cargoitself, it being understood that the cargo temperature may varyslightly, such as from 2 to 3 over various parts thereof, and also thatthe thermostat bulb 24- may be slightly above or be low the averagetemperature of the cargo, depending upon whether the cargo is beingcooled down or is heating up.

However, cargoes generally do not need to be maintained within afraction of a degree, since a range of temperature variation, such as 5or 6 F is usually permissible.

When the cargo has been cooled sufiiciently so that the thermostatresponds to its lower limit, the above circulation of cold air isterminated. However, in accordance with this invention, the blowers 21are not completely shut off, but are operated at a reduced speed, thatis, a speed sufiicient to produce very little, if any, circulation ofair to the cargo, but at the same time sufficient to cause the air tohang, as it were, in the control space S. This prevents the cold airfrom settling downwardly from the bunker B, to the floor of the trailer,and then passing rearwardly through the passage 20 at the bottom ofpartition P, to collect beneath and around the portion of the cargoadjacent the lower end of partition P. In the absence of movement pastthe bunker B, such air may be cooled to a very low temperature, and ifallowed to collect about the lower front end of the cargo C, may tend tounduly cool or freeze a portion of the cargo. If the cargo is packedsolid, the portion frozen will generally lie along the bottom, but ifthere are some air spaces between the various pieces of the cargo, thisextremely cold air will tend to collect adjacent the partition P. Suchcold air tends to freeze or cool unduly a portion of the cargo which mayextend over an area indicated generally by the dotted line 25 of Fig. 2.However, with the blowers 21 operating at reduced speed, such reverseflow of cold air is prevented, and the possibility of unduly cooling orfreezing a portion of the cargo is eliminated.

The refrigerant unit or bunker B, constructed in ac cordance with thisinvention, is provided with a plurality of shelves 26 which, as in Fig.2, providercon- 5 duction through metal to the side walls 27 of thebunker. The Dry Ice cakes, such as indicated by the dotted lines 28 ofFig. 2, are placed on the shelves 26, and due to the conduction throughmetal of heat from the side walls 27 to the shelves 26, very littleheat, such as only about 5%, will be transferred by convection directlybetween the cakes 28 and the side walls 27. Due to the greater rate ofheat conduction through metal, the bottoms of the cakes will receivenearly all of the heat, which will cause sublimation and reduction involume of the solid carbon dioxide, so that as the cakes are reduced tovolume, the area of contact, between each cake and the shelf 26 on whichit rests, will be maintained substantially constant. Thus, the cakeswill be reduced in height until only a small portion is left, such asrepresented by the dotted lines 28' of Fig. 2, but the contact areabetween the cakes and the shelves will remain substantially the same.The slight melting down at the sides and along the tops of the cakes,when the cakes have reached the volume represented by dotted lines 28,represents the small portion of heat transferred by convection orradiation. Due to the maintenance of the area in contact, the coolingeffect or refrigerating capacity of the bunker B will remainsubstantially the same throughout the effective life of the cakes. Thisis an important advantage, since a substantially uniform refrigeratingeffect permits the blowers to be run at a constant speed during cooling,with assurance that toward the end of a long run, for instance,

the cargo C will be just as effectively cooled as at the 7 start of therun, when the Dry Ice cakes are new. Thus, the cargo need not sufferbecause of reduced refrigerating capacity. It is to be noted that alarge reduction in refrigerating capacity, when the volume andconsequently the surface area of the cakes has been reducedconsiderably, has constituted a serious disadvantage of previousattempts to cool trailer cargoes and the like by means of solid carbondioxide ice, and has previously provided an advantage for mechanicalrefrigerating units. Thus, by use of the refrigerant unit or Dry Icebunker of this invention, this previous disadvantage has been overcome,and advantage may be taken of lower initial and operating costs and thesaving in pay load weight, when refrigeration is unnecessary, providedby the use of Dry Ice.

When solid carbon dioxide sublimates, carbon dioxide is of courseproduced. The resultant gas may be vented to the outside or to theinterior of the trailer, to add somewhat to the refrigerating effect,although the volume of the gas produced is relatively small incomparison with the amount of air circulated. Thus, a suitable pipe,

provided with a three-way valve operated from the exterior of thetrailer (neither shown) may be connected to the bunker B, so that theresultant carbon dioxide may be passed to the interior of the trailer orto the outside, as desired. The direction of venting of the gas willnormally be determined by the character of the cargo. Thus, there aresome cargoes, such as fresh meats, strawberries, cherries and the like,for which carbon dioxide gas is beneficial, i. e. CO2 tends to have aninhibiting effect on the action of enzymes and bacteria in such cargoes.However, in the case of certain fruits and leafy vegetables, CO2apparently tends to have a detrimental effect, so that the bunker shouldbe vented to the outside for such cargoes.

In order to provide adequate conduction of heat through metal betweenthe shelves 26 and the side walls 27, each shelf 26 may be made integralwith a section of the side wall. As in Fig. 2, the lower end of eachsection may be reduced in width, at the shelf, so that the sections willbe interfitting. Or, as in Fig. 5, each side wall 27 may be made of asingle piece or sheet of metal, and the shelves 26 riveted thereto onthe inside, with relatively wide flanges on the shelves to providesufficient metal to metal contact between the shelf 26 andthe side wall27'. To increasethe transfer of heat from the air passing therearound,the side walls 27 and also the rear end 29 of the bunker B, as in Figs.2-4, may be provided with outwardly extending fins 30, each having ashort leg riveted to the side wall or end of the bunker and a longer legextending outwardly therefrom. Also, at spaced positions about thebunker, posts 31 or the like, such as Z-section posts as in Figs. 3 and4, may be riveted to the bunker Wall to support the bunker B above thetrailer floor 17, to permit air to pass under the same. The posts 31along the forward wall may be conveniently secured, as by riveting, tothe front wall 18 of the trailer, while the posts 31 along the rear wallmay conveniently support the partition P. The central posts 31 may alsoextend above the top 32 of the bunker, to provide support for theblowers 21 and a heater H, while the fins 30 are preferably providedonly on the sides and the end of the bunker, since a considerablygreater amount of heat is transferred to the air from the fins and byomitting fins on the bottom and top of the bunker, all the cakes willtend to sublimate in synchronization. Of course, if the lower cakessublimate too rapidly, then the tin arrangement may be altered, or otherchanges made. It is to be emphasized, of course, that the heat transferis, as far as possible, substantially exclusively by conduction throughmetal from the side walls to the shelves on which the cakes rest.

As in Fig. 3, bunker B may be open at one end for loading purposes, andthe trailer T is conveniently provided with an insulated door 34 whichmay be opened to place ,Dry ice cakes in the bunker, to remove theresidue of cakes, or for cleaning and inspection purposes. The loadingedge of each shelf 26 may also be reinforced by an angle 35, as in Fig.2, or other suitable means to withstand the Dry Ice cakes being bouncedor slammed on the loading edges. in an available commercial size, DryIce cakes are about ten inches by ten inches square and from abouteleven inches to thirteen inches in height, weighing about fifty tofifty-seven pounds apiece. Each shelf 26 may be designed to take anydesired number of cakes, seven cakes to each shelf being the capacity ofa bunker used in cooling large trailers on a long run. As will beevident, the three shelves will take 21 cakes, and if refrigeration isnot needed, the weight available for pay load is at least 21 x 50 or1050 poundsover one-half ton. In addition, the total weight of arefrigeration unit constructed in accordance with this invention is lessthan a mechanical unit of similar capacity. For example, the weight ofthe 21 cake unit mentioned above is only 500 lbs., which is between /2and /3 of the weight of mechanical units of approximately equivalentcapacity.

The door 34 need extend only to the top of the bunker and when closed,the space between the open end of the bunker and the door is preferablyoccupied by an insulating bag 36 which covers the open end of thebunker, as in Pig. 3. Of course, the loading end of the bunker may beclosed by hinged doors, or other suitable means to render the bunkermore nearly gas tight, if desired. However, the insulating bag 36 may bepressed in about the edges of the bunker openings so as to provide aneffective seal, when the CO2 is to be vented to the outside. When theCO2 is to pass to the interior of the trailer, the insulating bag may beleft slightly ajar at one edge to provide egress for the gas produced bysublimation. The bunker B may, of course, be made so as to be loaded atthe center, in which case the loading door will be located in the frontwall 18 of the trailer, and an insulating bag may or may not be used, asdesired. Of course, one advantage of end loading is that the side wallsover the center space can conduct heat through metal to the shelves,whereas if center loading is employed, either an open space in the frontof the bunker or doors for access to the shelves will tend to reduce thecooling capacity of that area of the side walls.

The blowers 21 and motor 22, as in Figs. 3, 6 and 7, may be mounted on aseries of bars or angles 37 or the like, extending between the centralposts 31, which in turn extend above the top 32 of the bunker B, asindicated previously. The blowers 21 are conveniently two in number,each of which has a pair of opposed axial intakes and a circumferentialdischarge. A pair of blowers not only provide a better distribution ofthe discharged air, but also tend to provide better balance for themotor 22, since a blower may be mounted on each end of the motor shaft.However, it will be understood that only one, or more than two, or otheror diiferent types of blowers or air circulators may be utilized. Theheater H may also be mounted on bars or angles 37, similarly extendingacross and/or between the central posts 31, above the top of the bunkerbut below blowers 21, although the heater may be placed in otherpositions.

The heater H may be of a conventional type and include, as in Fig. 6,air intake ports 38 leading to a motor driven fan (not shown), whichcauses the air to pass through a heating section in which a fuel, suchas gasoline or fuel oil, is burned, the fuel being supplied to theheating section through a float controlled inlet 39 and the products ofcombustion exhausted through a pipe 40, shown also in Fig. 1. Pipe49'extends to the outside, such as across the top of the bunker B, thendown along the closed end and through the floor of the trailer. Also,fuel may be supplied through a tube 41 which extends to inlet 39 from aconvenient source of supply, such as the fuel tank 42 of the generatingunit G, as in Fig. l, a suitable pump or the like (not shown) beingprovided at tank 42. A control thermostat 43, for the heater, may bemounted adjacent the intake end thereof, and operated to turn the heateron and off, in accordance with the air temperature within the trailer,and more particularly in the control space S. During heating, theblowers 2 preferably operate continuously to minimize Stratification andproduce an even temperature distribution for the full length of thecargo, although other control systems may be utilized.

Since the heater and blowers may at times require inspection ormaintenance, particularly since the same include moving parts, arelatively large inspection door 44 is preferably provided in the frontwall it; of the trailer, as in Fig. 2, so that access to the blowers andheating unit may be obtained without the necessity of disturbing anypart of partition P,'or any part of the cargo. Access to the heater andblower unit through the Dry Ice loading door 34 is not preferred, thoughpossible, since the space around the blowers and heater unit is ratherlimited.

As indicated previously, the thermostat bulb 24, for use in controllingthe cooling cycles, is preferably positioned near the top of thetrailer, at the front of the cargo space, since normally the warmestspot in the cargo space will be at this point, due to the lower specificgravity of Warm air and the higher specific gravity is cold air, as thelatter tends to settle to the bottom and to the rear of the trailer.When the outside temperature is lower than that desired for the cargo,and heating is required, the coldest spot will generally be at thefloor, at the rear end of the trailer, but when the blowers maintain aircirculation at all times, the temperature will be more nearly uniformthroughout the trailer, so that the location of the heater thermostat 43adjacent the heating unit H provides a sufiiciently accurate indication,for practical purposes, of the temperature of the cargo.

Whcnthe thermostat bulb 24 for controlling cooling is located near theroof, on the inside, an expansion line, such as tube 45, may lead to acontrol unit do, which may include a bellows and control switch, thesame being conveniently disposed in a post office box 47 or similaraccessible position on the outside of the trailer, as in Fig.

3. The post oifice box" may be provided with a door, to provideaccessibility for setting the temperature controls, at predeterminedlimits, and also for changing from cooling to heating-and vice versa.The thermostat bulb 24 is connected by tube 46 with control unit 45 andmay be the conventional type, wherein the coldest point in the bulb ortube influences the control unit. It may sometimes happen that the upperportion of the cargo, as received by the shipper, will be warmer thanthe lower portion of the cargo and require cooling. To preclude thepossibility of the thermostat being artificially satisfied because ofunprotected proximity of a lower or colder portion of the cargo to tube46, the tube should pass upwardly through the insulation of side wall 15of the trailer until relatively close to bulb 24.

The blower motor 22 and the heater H are preferably operatedelectrically, and electricity may be supplied thereto from the tractorfor the trailer, but it is preferred to install a governor-controlled,gasoline driven, generating unit G beneath the trailer, as in theposition shown in Fig. 1. This generating unit G permits the refrigerantunit to be operated while the trailer is not connected to a tractor,such as at a loading dock when a cargo is being loaded thercinto, andthus is particularly valuable when the cargo being loaded is warm butshould be cooled down as soon as possible. In addition, the generatingunit relieves the tractor generator and battery of a continuous drain,since electricity for the blowers and/ or heating unit may comprise agreater load than for which the battery or generator of the tractor unitmay be designed, except for temporary operation. Thus, a standbyemergency line is preferably provided so that electricity may besupplied temporarily from the tractor in case the generating unit stopsand cannot be started within a suitable time.

The control of the two speed or variable speed motor 22 may be achievedthrough any suitable circuit, an illustrative example being showndiagrammatically in Pig. 3. The motor 22-, represented by its rotor andbrushes, may be a direct current, compound wound motor having a seriesfield 5i) and shunt field 51, the former being connected to ground, asby a wire 52, and the latter to a junction 53, as by a wire 54. Astarting relay coil 55 may control a switch 56 in a line wire 57 leadingto junction 53, while a thermostat control unit 5' (represented asincluding also a temperature bulb) may be connected in series with arelay coil 58, as bywires and 6%}, which controls a switch 61. Switch 61is interposed in a line 62, leading from junction 53 to a secondaryjunction 63, connected by a Wire 64 with the armature of motor 22. Whenthe thermostat control 45' is actuated by the tcz'nperaturc reaching thehigh setting, cooling thereby being required, the thermostat contacts(not shown, being conventional) will cause current to be supplied torelay coil 58, which when energized will cause switch 61 to be closed.With switch 61 closed, full line current will pass through the armatureof motor 22, so that the motor will turn at its higher speed. However,when the temperature drops so that the lower limit of thermostat control45 is reached. the contacts thereof will open, causing relay coil 58 tobe tie-energized and switch 61 to open. Current to the armature of motor22 then will pass only through a resistance 65, connected betweenjunctions 53 and 63, thus reducing the amount of current flowing to themotor armature and reducing the speed thereof. The value of resistance65, which may be made variable resistance if desired, is preferablyproportioned to the amount of current necessary to cause the motor toturn over relatively'slowly and thereby cause the blowers to operate asufilciently low speed that little or no circulation of air through thecargo space of the trailer is produced, but at the same time keep theair suspended or hanging in the control space S, shown in Fig. 2. Thus.there will be no tendency for extremely cold air to drift into the cargospace and unduly freeze or cool portions of the cargo. It will beunderstood, of course, that other control circuits may be 9 utilized,for controlling the operation of the two speed or variable speed motor.

The circuit for controlling the heater may be provided in any suitablemanner, an illustrative example being shown in the wiring diagram ofFig. 9, in which certain parts may be incorporated in, or may be addedto, the control circuit for cooling, such as that shown in Fig. 8. InFig. 9, block 67 represents the starting relay for both blower motor andheater, block 68 represents the heater, and block 69 represents thenormal cooling thermostat control device. Wires 7%) and '71 represent,respectively, the full speed and reduced speed leads to the main blowermotor 22, while line wire 72 connects relay 67 with thermostat 69. Whenclosed, due to cooling being called for, thermostat control 69 willnormally connect line wire 72 with the blower motor through full speedwire 70, but when open will connect only reduced speed wire '71, whichincludes a resistance or the like, with the blower motor. A double poleswitch having blades 73 and 7 2 is therefore provided, so that whenclosed, blade 73 will connect a wire 75, leading from wire 70, with awire 76, leading to wire 71, so that the blower motor will run at fullspeed when current is supplied to the heater, irrespective of theposition of thermostat 69. in addition, switch blade 7 when closedconnects a branch wire 77 of wire 75 with a wire 78 leading to heater68. The operating circuit for the heater is, of course, in series withthe contacts of the heater thermostat 43, so that the operation of theheater will be intermittent, depending upon the temperature of the airwithin the control space. It will be understood, of course, that othercircuits, such as an independent circuit for the heater and a shortcircuiting switch for the full speed blower motor connection, may beutilize There are, of course, variations which may be made in the methodand apparatus of the present invention, and particularly in the mannerin which a back flow of cold air to the cargo space may be preventedduring the cooling interruption periods. Thus, apparatus claimed in andparticularly adapted to carry out the method claimed in said Patent No.2,5 89,031 is illustrated in Fig. 10, in which the bunker B, thepartition P, and vents 23 are similar to those of Figs. 1-5. However,the blowers 21 of Fig. 10 are adapted to be run at full speed during allthe time and may have intakes on only the inner sides. The bunker B ismounted within a bell or open bottom enclosure 80 which providespassages at the sides and at one end, to permit air to pass between thefins 30. Bell 80 is also provided with an upwardly converging top 81which leads to a duct 82, connected with the intake of the blowers 21,or a separate duct for each blower may be provided, if desired. One sideof duct 82 is provided with a gate 83, preferably hinged at the bottomand adapted to be opened or closed by suitable means, such as ahydraulic cylinder 84. With gate 83 in the position shown, i. e.,closing duct 82 against the flow of air from the bunker'B, butpermitting air to flow into the duct and to the blowers from the controlspace S, above hell 8%, air will be discharged into the cargo space bythe blowers and will be withdrawn from the bottom of the cargo space,but will pass underneath the bunker B and through a passage 85 formedbetween the front wall 18 of the trailer and the front wall of bell 80,which is preferably provided with insulation 86. Thus, between coolingperiods, the air will be by-passed around the bunker B. Also, any coldair settling downwardly from the bunker B will be mixed with the airpassing therebeneath and will not settle beneath the cargo at the frontlower end of the cargo space. However, the amount of cold air which willbe mixed with the air bypassed around the bunker will be relativelysmall, so that no undue cooling effect will tend to be produced. Theoperation of hydraulic cylinder 84 may be by a suitable thermostatcontrol device, such as that previously described. Of course, provisionmust be made for supplying oil or other suitable liquid to the cylinder84, so that an electromagnet may, if desired, be utilized instead of a10 hydraulically operated device. Preferably, the gate 83 is mounted soas to be in either one position or the other, i. e. opened or closed,although provision can be made for controlling the amount of cooling bymoving the gate to different intermediate positions.

It will be understood, of course, that other changes and variations maybe made, as for instance mounting the heater outside the trailer andconnecting the same to two different points of the control space, sothat air from the control space will pass through the heater from onepoint and the heated air will enter the control space at another point.Normally, the fan incorporated in the heater has insufficient power tocause the desired circulation of air through the cargo space, so thatthe blowers 21, which normally have considerably greater capacity thanthe heater fan, are preferably utilized for such circulation. The bunkershelves may be loaded from the center or from either end, although endloading is normally more convenient. Also, a single blower may be used,although two or more blowers tend to distribute the air more nearlyequally across the space at the top of the cargo. It will be understood,however, that the blowers may be located at other positions, as long asan adequate circulation of air about the cargo and about the coolingunit is maintained.

From the foregoing, it will be evident that the method and apparatus ofthis invention fulfill to a marked degree the requirements and objectshereinbefore set forth. By passing the air, either for cooling orheating, along the top of the cargo, through spaces along both sides andat the opposite end of the cargo, as well as beneath the cargo, thetemperature of all points of the cargo can be maintained more nearlyuniform. A heating and/or cooling unit may be installed in any desiredposition, although a position at the front of a truck or trailer, forinstance, tends to interfere least with access to the cargo. The coolingunit is preferably disposed in a space which is separated from the cargoby a properly insulated partition, and an important feature of thisinvention is the prevention of a backflow of cold air to the cargoduring the off periods of the cooling cycle. This is preferably carriedout by operating the blowers at a reduced speed, sufficient merely tocause the air to hang, as it were, about the cooling unit.

By placing the heater in the control space, additional cargo space canbe provided, but the heater may be located in any other desiredposition. However, during heating, it is of considerable advantage tooperate the blowers normally used to circulate cooled air about thecargo, since an effective transfer of heat to the air from the cargo, orvice verse, is essential.

When the temperature of various points of the cargo can be maintainedmore nearly uniform, and undue cooling or freezing of certain parts ofthe cargo prevented, then a solid refrigerant which sublimates, such assolid carbon dioxide, with its attendant advantages, can be utilized.For effective refrigeration, it is highly desirable that therefrigerating or cooling capacity be maintained at a relatively highlevel during the entire period of use, since a sharp reduction in suchcapacity, toward the end of a particular period, may result in a loss orspoilage of cargo. A solid refrigerant heat transfer unit or bunker,constructed in accordance with this invention, fulfills theserequirements. When the Dry Ice cakes are placed on shelves or the like,conduction of heat is through metal from the side walls, which arepreferably provided with fins to increase the amount of heat transferredfrom air passing thereover, the rate at which the carbon dioxide cakessublimate may be made more nearly uniform for all shelves in amulti-shelf unit. Thus, a relatively uniform refrigerating effect is theresult of a cooling surface whose area and temperature remain relativelyconstant.

The control point for the cooling thermostat is preferably disposed nearthe top, adjacent the forward end of the cargo space, and it is moreconvenient to place the controls in a more accessible position, such asin a post 1 1 office box or the like on the outside of the trailer.However, the line from the bulb to the control bellows should beinsulated, such as by extending through the insulation of the sidewallsof the trailer or the like, so that an initially colder portion of thecargo, if at the lower front end of the cargo space, will not produceerratic control action.

Although certain specific embodiments of this invention have beenillustrated and described, it will be understood that other embodimentsmay exist and various changes made therein, all without departing fromthe spirit and scope of this invention.

What is claimed is:

1. Apparatus for controlling the temperature of trailer cargo and thelike, comprising a wall defining a space at the forward end of saidtrailer or the like, said wall being spaced from the bottom of saidtrailer by an opening and having at least one air discharge openingadjacent the top; a Dry Ice bunker for cooling air to a temperaturebelow that of the desired temperature of said cargo, said wall beinginsulated between said bunker and said cargo; continuously operating airimpulse means for imparting an impulse to said air at least at one pointabove said bunker normally to effect a circulation of air by drawing airfrom the lower portion of said cargo space through said lower openingand upwardly along said bunker and then discharging said air into saidtrailer through said top discharge opening so that said air passesaround said cargo to cool the same and then returns to said loweropening for recirculation, said air impulse means also being 0perable ata lower rate of air impulse which produces not more than very littlecirculation of air through said cargo space but is sufficient to preventa hack flow of cold air from said bunker to the lower portion of saidcargo; and means for controlling said air impulse means in accordancewith the temperature in said cargo space so that said air impulse meansoperates at said higher rate when cooling is required and at said lowerrate when cooling is not required.

2. Apparatus for controlling the temperature of trailer cargo and thelike, comprising a wall defining a space at the forward end of saidtrailer or the like, said wall being spaced from the bottom of saidtrailer by an opening and having at least one air discharge openingadjacent the top; a Dry Ice bunker for cooling air to a temperaturebelow that of the desired temperature of said cargo, said Wall beinginsulated between said bunker and said cargo; a blower disposed abovesaid bunker and having an air intake within said forward space and adischarge conduit connected with the discharge opening in said wall;continuously operating drive means for said blower having at least twospeeds, including a higher speed for drawing air upwardly along saidcooling unit and discharging said air into said trailer above saidcargo, so that said air passes around said cargo to cool the same andthen returns to the opening beneath said wall for recirculation, and alowor speed which tends merely to cause air to hang in said coolingspace without appreciable discharge over and cooling of said cargo, sothat the tendency for cold air to settle downwardly from said coolingunit and pass through said opening to cool unduly portions of said cargois prevented; and means controlling said drive means in accordance withthe temperature in said cargo space, so that said drive means operatesat said higher speed when cooling of said cargo is required and at saidlower speed when cooling is not required.

3. Apparatus for controlling the temperature of trailer cargo and thelike, comprising a wall defining a space at the forward end of saidtrailer or the like, said wall being spaced from the bottom of saidtrailer and having at least one air discharge opening adjacent the top;a refrigeration unit for cooling air to a temperature below that of thedesired temperature of said cargo, said Wall being insulated betweensaid unit and said cargo, said unit being a metal compartinentedstructure having vertical side walls and a plurality of generallyhorizontal shelves therein,

said shelves having a metal to metal heat conductivity relationship withsaid side walls, so that a block of solid deliquescent refrigerantplaced on a shelf will absorb heat from said side walls substantiallyexclusively by conduction and as said block deliquesces and becomessmaller, the bottom area of said block in contact with said shelf willbe maintained substantially constant during a majority of thesublimation time of said block; a blower disposed above said coolingunit and having an air intake within said forward space and dischargeconduit connected with the discharge opening in said wall; and drivemeans for said blower having at least two speeds, including a higherspeed for drawing air upwardly along said cooling unit and dischargingsaid air into said trailer above said cargo, and a lower speed whichtends merely to cause air to hang in said cooling space withoutappreciable discharge to said cargo.

4. Apparatus for controlling the temperature of trailer cargo and thelike, comprising a wall defining a space at the forward end of saidtrailer or the like, said wall being spaced from the bottom of saidtrailer and having at least one air discharge opening adjacent the top;a refrigeration unit for cooling air to a temperature below that of thedesired temperature of said cargo, said wall being insulated betweensaid unit and said cargo, said unit being a metal compartmentedstructure open at one end and having vertical side walls and a pluralityof generally horizontal shelves therein, said shelves having a metal tometal heat conductivity relationship with said side walls, so that ablock of solid deliquescent refrigerant placed on a shelf will absorbheat from said side walls substantially exclusively by conduction and assaid block deliquesces and becomes smaller, the bottom area of saidblock in contact with said shelf will be maintained substantiallyconstant during a majority of the sublimation time of said block; a doorin said trailer providing access to the open end of said cooling unit;an insulating bag for filling the space between said door and said endof said unit; a blower disposed above said cooling unit and having anair intake within said forward space and discharge conduit connectedwith the discharge opening in said wall; and drive means for said blowerhaving at least two speeds, including a higher speed for drawing airupwardly along said cooling unit and discharging said air into saidtrailer above said cargo, and a lower speed which tends merely to causeair to hang in said cooling space without appreciable discharge to saidcargo.

5. In temperature control apparatus, a unit for cooling air and the liketo a relatively low temperature by means of a solid deli-quescentrefrigerant, which comprises means defining an enclosure havinggenerally vertical side walls; an enclosed, ccmpartmented metalstructure disposed within said enclosure means and having a top, abottom, side walls and end walls, said side walls being vertical and atleast said side walls and said bottom being in spaced relation to theside walls and bottom of said enclosure, said structure being providedwith an access door for placing cakes of a solid deliquescentrefrigerant therein and said side walls having a substantially greatertransverse dimension than said end walls, said structure including aplurality of generally horizontal shelves therein with said bottomforming one of said shelves, each of said shelves having a metal tometal heat conductivity relationship with said side walls so that ablock of solid deliquescent refrigerant placed on a shelf will absorbheat from said side walls substantially exclusively by conduction and aseach said block deliquesces and becomes smaller, the bottom area of saidblock in contact with said shelf will be maintained substantiallyconstant during a majority of the sublimation time of said block; andmeans for drawing air upwardly through the spaces between the side wallsof said structure and the side walls of said enclosure means.

6. In temperature control apparatus, a unit for cooling air and the liketo a relatively low temperature by means of a solid deliquescentrefrigerant, as defined in claim 5,

13 wherein each said shelf is integral with a section of the side wallthereabove.

7. In temperature control apparatus, a unit for cooling air and the liketo a relatively low temperature by means of a solid deliquescentrefrigerant, as defined in claim 5, wherein said shelves above saidbottom are attached to said side walls in intimate metal to metalcontact.

8. In temperature control apparatus, a unit for cooling air and the liketo a relatively low temperature by means of a solid deliquescentrefrigerant, which comprises means defining an enclosure havinggenerally vertical side walls; an enclosed, compartmented metalstructure disposed within said enclosure means and having a top, abottom, side walls and end walls, said side walls being vertical and atleast said side walls and said bottom being in spaced relation to theside walls and bottom of said enclosure, said structure being providedwith an access door for placing cakes of a solid deliquescentrefrigerant therein and said side walls having a substantially greatertransverse dimension than said end walls, said structure including aplurality of generally horizontal shelves therein with said bottomforming one of said shelves, each of. said shelves having a metal tometal heat conductivity relationship with said side walls, so that ablock of solid deliquescent refrigerant placed on a shelf will absorbheat from said side walls substantially exclusively by conduction and assaid block deliquesces and becomes smaller, the bottom area of saidblock in contact with said shelf will be maintained substantiallyconstant during a majority of the sublimation time of said block, saidstructure including a plurality of vertically disposed fins attached toand extending outwardly from at least said walls and no fins extendingfrom the bottom of said structure; and means for drawing air upwardlythrough the spaces between the side walls of said structure and the sidewalls of said enclosure means.

9. A method of controlling the temperature of trailer cargoes and thelike, to be cooled by a low temperature refrigerant having a temperaturesufliciently lower than the lowest temperature to which the cargo is tobe cooled that a portion of the cargo may be frozen by uncontrolledcooling and wherein said refrigerant is disposed in heat transferrelationship to an air cooling space disposed at an elevation above thelower portion of said cargo space and through which air may be passed,said method comprising imparting an impulse to said air at least at onepoint above said air cooling space, normally to effect a circulation ofair by drawing air from the lower portion of the cargo space andupwardly through said air cooling space, then passing said cooled air tosaid cargo space to cool said cargo and to the lower portion of saidcargo space, and thence back to said cooling space; controlling saidimpulse to said air so as to effect a higher rate of air circulationwhile at least one control point responsive to the temperature in saidcargo space is above a first predetermined temperature; and reducing theimpulse to said air when said control point is below a secondpredetermined temperature, said second predetermined temperature beinglower than said first predetermined temperature and such reduction inimpulse being effected to a value which produces not more than verylittle circulation of air through said cargo space but which issufiicient to prevent a back flow of cold air from said air coolingspace to the lower portion of said cargo, some impulse to said air beingeffected at all times during cooling operations.

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